In recording a hologram, if an object is close to a recording medium, reference light will not be introduced conveniently. Hence, it is usual to produce image light by way of imaging, and allow the image light to interfere with the reference light to complete the recording of the hologram. There are usually two schemes for image surface hologram recording: one is to employ a lens imaging method, and the other is to employ a two-step recording method.
FIG. 1 is a schematic view of a lens imaging method. According to the lens imaging method, a lens 2 is used to image an object 1 to produce image light, and then interference stripes of the image light with the reference light are recorded on a holographic plate 3 to implement the recording of the image surface hologram. This method is the one-step hologram recording method, which does not require a complicated light path. However, due to limitations of a lens manufacturing process and an aperture, the image surface hologram recorded by this method may distort with a small angle of field of view.
FIGS. 2a and 2b are schematic views of a two-step recording method. According to the two-step recording method, a Fresnel hologram H1 is usually recorded for an object 1 first, then conjugate light (reconstruction light as shown in FIG. 2b) of the reference light is used to illuminate the hologram H1 to reconstruct an objective image 4, and the image light of the objective image 4 is superimposed with the reference light to obtain an image surface hologram H2. This method comprises two times of recording and one time of reconstruction, which is complicated in operation and has large noises.